Lighting device

ABSTRACT

In one embodiment of lighting devices and lighting systems, the lighting device has a connection for connecting to a primary power supply and has a secondary power supply, such as a battery. A measuring circuit is operable to measure an impedance of the primary power supply connection and to determine from the measurement if a main power supply has failed, and if so whether to power light sources using power from the secondary power supply.

BACKGROUND

The present invention relates to lighting devices and in particular tolighting devices that have additional components and circuitry to enablethe lighting device to emit light using electrical energy from asecondary power supply (such as a battery) if the primary power supply(such as a mains supply) is interrupted.

In the event of an electrical power supply failure to a conventionallighting device, the absence of any immediate or sustained ambient lightpresents numerous safety, welfare, convenience and security concerns tothe occupants of any affected public, commercial, industrial orresidential buildings and areas. Existing standby or emergency lightingsystems typically take the form of a bespoke unit, primarily designedfor industrial and commercial environments, which solely function in theevent of a power failure (power outage). These existing productstypically require dedicated installation, additional wiring and regularmaintenance and testing, adding further to purchase and ownership cost.Light is usually only produced in the event of a mains power failure anduntil either the secondary source is exhausted or primary power isrestored, and during that time the user cannot control the lightreadily, such as to conserve the limited electrical storage capacitywhen light is not required. Further still, these lighting devices areusually functionally termed “non-maintained” and are only intended togive emergency rather than mainstream illumination when the primarymains power supply is available. Therefore, the associated emergencylighting apparatus is operationally redundant whenever mains power isavailable and primary lighting is used instead.

Some existing lighting devices are arranged to produce uninterruptedprimary illumination from either primary or secondary supplies. Thesedevices are termed “maintained”. In antithesis, lighting devices termed“maintained” are generally intended to produce uninterrupted primaryillumination sustained from either mains or secondary electrical storagesources. Maintained devices typically have no switch on supply, hencerequire permanent mains feed, thus light is usually continuous with thebattery being used if the permanent mains feed fails.

The above problems can be solved by combining standard and emergencylighting into one unit that may retro-fit any existing non-emergencylight fitting or wiring installation and which may replace or augmentany conventional lighting devices powered from the mains power supply.

The present inventor has previously proposed (in GB 2447495) an electriclighting device having circuitry that can detect mains failure and whichcan provide power to the lighting device from a backup battery providedin or close to the lighting device. One important function of thisearlier lighting device is that it is able to distinguish between afailure in the mains power supply and a user controlled removal of thepower supply at a light switch. As described in the inventor's earlierGB application, this is achieved by evaluating the impedance across thesupply terminals. When there is a mains power failure and the light isswitched on, the impedance will be low; whereas when the user hasswitched off the light at a light switch the impedance will be high.

The present application describes a number of improvements to thelighting device described in the inventor's earlier GB applicationdiscussed above.

SUMMARY OF INVENTION

According to one aspect, the invention provides a method of controllinga lighting apparatus comprising one or more light sources, a primaryinput power connection for receiving primary power from a primary powersupply, for powering a light source, a secondary input power connectionfor receiving secondary power from a secondary power supply, forpowering a light source, the method comprising: controlling powerdelivery to the one or more light sources using power received at theinput power connections, such that in the event of a power failure,power from the secondary power supply is used for powering a lightsource; sensing an external impedance connected to the primary inputpower connection by applying measurement pulses to the primary inputpower connection to obtain an impedance measure of the externalimpedance; and wherein the controlling step controls the power deliveryin dependence upon the impedance measure.

The sensing may apply the measurement pulses to the primary input powerconnection and detect transient signals on the primary input powerconnection, from which a measure indicative of the external impedanceconnected to the primary input power connection is determined. Themeasure can then be used to determine if manually operable switchescoupled to the primary input power connection are in an open or a closedstate. Based on this determination, the method can distinguish between:i) removal of the primary supply from the primary input power connectionby a user opening a switch coupled, in use, to the lighting apparatus;and ii) primary supply failure; and, upon detection of primary supplyfailure, can provide power from the secondary power supply to the lightsource to provide emergency lighting functionality.

The duration and/or the time period between measurement pulses that areapplied to the primary input power connection may be varied. This may bedone in dependence upon a charge status of the secondary power supplyor, where the lighting apparatus has a plurality of different modes ofoperation, in dependence upon the time that the lighting device has beenin a present mode of operation or in a random or pseudo-random manner.

The method may determine a measurement of the external impedance for aplurality of measurement pulses and may combine two or more of thosemeasurements to determine an average measurement. The method may involveapplying measurement voltage pulses and/or measurement current pulses tothe primary input supply connection.

The present invention also provides a lighting control apparatuscomprising: a primary input power connection for connection to a primarypower supply; a secondary input power connection for receiving secondarypower from a secondary power supply; and electronic circuitry arrangedto control power delivery to one or more lighting devices; wherein theelectronic circuitry comprises sensing circuitry configured to sense anexternal impedance coupled, in use, to the primary input powerconnection and wherein the sensing circuitry is arranged to applymeasurement pulses to the primary input power connection to obtain animpedance measure of the external impedance and wherein the electroniccircuitry is arranged to control power delivery to the one or morelighting devices in dependence upon the impedance measure.

The electronic circuitry is arranged to apply the measurement pulses tothe primary input power connection and is arranged to detect transientsignals on the primary input power connection, from which it determinessaid impedance measure. The sensing circuit can determine the impedancemeasure based on a decay rate of the transient signals. The sensingcircuit may determine a time period for the transient signals to decayfrom a first level to a second level and use this as the impedancemeasure. One or both of the first level and the second level may besystem constants or system variables that are dynamically set based on anumber of previous measurements obtained by the sensing circuitry.

The electronic circuitry can use the impedance measure to determine ifmanually operable switches coupled to the primary input power connectionare in an open or a closed state.

In one embodiment, the sensing circuitry compares the impedance measurewith a threshold value and based on the result of the comparisondetermines if manually operable switches coupled to the primary inputpower connection are in an open or a closed state. The threshold may bea system constant or a system variable that is dynamically set based ona number of previous impedance measurements. Based on the determination,the electronic circuitry can distinguish between: i) removal of theprimary supply from the primary input power connection by a user openinga switch coupled, in use, to the control apparatus; and ii) primarysupply failure; and, upon detection of primary supply failure, thecircuitry can control power delivery to the one or more lighting devicesusing power from a secondary power supply to provide emergency lightingfunctionality.

The electronic circuitry can vary the duration and/or the time periodbetween measurement pulses that are applied to the primary input powerconnection. This variation may be in dependence upon a charge status ofthe secondary power supply; in dependence upon the time that theelectronic circuitry has been in a present mode of operation; or in arandom or pseudo-random manner.

The electronic circuitry may determine a measurement of the externalimpedance for each of a plurality of measurement pulses and may combinetwo or more of those measurements to determine an average measurement.

The sensing circuitry can apply measurement voltage pulses and/ormeasurement current pulses to the primary input supply connection.

In one embodiment, the electronic circuitry obtains a measurement of avoltage level and/or frequency of a power signal received at the primaryinput power connection and if the measured voltage level or frequency iswithin a predefined range, inhibits operation of the sensing circuitry.

The electronic circuitry may have a sleep mode of operation in which thesensing circuitry is inoperative and wherein the electronic circuitry isarranged to wake up from the sleep mode upon application of a powersignal to the primary input power connection or upon receipt of anexternal control signal.

The sensing circuitry may hibernate between measurement pulses.

In one embodiment, a capacitor is coupled to the primary power inputconnection and the sensing circuitry monitors the charge on thecapacitor resulting from the application of the measurement pulse to theprimary power input connection. The sensing circuitry can, for example,monitor the way in which the charge accumulates on the capacitor duringapplication of the measurement pulse and from the monitored chargeaccumulation estimate the number of other electronic devices coupled tothe primary input power connection.

The secondary power input connection is for receiving power for theelectronic circuitry from a secondary power supply when power is notavailable at said primary power input connection; and the electroniccircuitry can inhibit operation of the sensing circuitry if a remainingcharge of the secondary power supply is below a threshold value.

In one embodiment, an isolator is provided that can isolate theelectronic circuitry from the primary input power connection.

A power supply unit may be provided that receives primary power from theprimary input power connection and which provides a rectified primarypower supply for powering the electronic circuitry and furthercomprising circuitry arranged so that the larger of rectified primarypower supply and the secondary power supply is used to provide power toa processor forming part of said electronic circuitry.

The lighting device described above may be provided in a housing adaptedfor connection in a conventional lighting circuit between supply wiringand a conventional lamp holder.

The conventional lamp holder may be an AC lamp holder and the electroniccircuitry may provide an AC output supply obtained from an AC inputsupply received at the primary input power connection to outputconnections used to connect to the conventional lamp holder to supplythe AC output supply to the conventional lamp holder.

The conventional lamp holder may also be a DC lamp holder and whereinthe electronic circuitry may convert an AC supply received at theprimary input power connection to output a DC supply on outputconnections used to connect to said conventional lamp holder to supplysaid DC supply to said conventional lamp holder.

The electronic circuitry may include an isolator for isolating theoutput connections when the sensing circuitry is measuring the externalimpedance.

The electronic circuitry may supply power to a plurality of outputconnections of the housing to provide power to a plurality of lampholders and wherein the electronic circuitry may provide, in the eventof primary supply failure, power from the secondary power supply to asubset of the output connections.

The control apparatus may send a control signal to the one or morelighting devices to control the delivery of power to the one or morelighting devices. The control apparatus may send the control signal tothe one or more lighting devices over a wireless link or over a primarysupply line connected, in use, to the primary input power connection.

The invention also provides a lighting device comprising: one or morelight sources; and the above control apparatus. The lighting device mayinclude one or more primary light sources for use in providing primaryillumination and one or more secondary light sources for providingsecondary illumination and may further comprise a sensor for sensingillumination failure of one or more of the primary light sources. Theelectronic circuitry may switch on one or more of the secondary lightsources in the event that the sensor detects illumination failure of oneor more of the primary light sources. The electronic circuitry canswitch on the one or more secondary light sources until it detects achange in the availability of primary power at the primary input powerconnection. The sensor may be selected from the group comprising: a loadsensor, an impedance sensor and a light sensor.

The present invention also provides a kit comprising: the above controlapparatus for generating and transmitting a control signal forcontrolling the application of power to one or more lighting devices;and one or more lighting devices, each comprising: a primary input powerconnection for connection to a primary power supply; a secondary inputpower connection for receiving secondary power from a secondary powersupply; and electronic circuitry arranged to receive the control signalfrom the control apparatus and arranged to control the delivery of powerto the one or more light source(s) using power from the primary inputpower connection or using power from the secondary input powerconnection in dependence upon the control signal received from thecontrol apparatus.

Another aspect provides a lighting device comprising: one or more lightsources; a primary input power connection for receiving primary powerfrom a primary power supply, for powering a light source of the lightingdevice; a secondary input power connection for receiving secondary powerfrom a secondary power supply, for powering a light source of thelighting device; and electronic circuitry configured to control powerdelivery to the one or more light sources using power received at one ormore of the input power connections; and wherein the electroniccircuitry has a primary mode of operation in which primary power isavailable at the primary input power connection and a secondary mode ofoperation in which primary power is not available at the primary inputpower connection, and wherein the electronic circuitry has a pluralityof user configurable parameters defining different brightnesspreferences for the primary operating mode and the secondary operatingmode.

The electronic circuitry may vary the brightness of the light generatedby the lighting device by varying the power supplied to one or more ofthe light sources and/or by varying the number of light sources thatreceive power from the primary and/or secondary supplies.

The electronic circuitry may receive a signal over a wirelesscommunications link or through one or more of the input powerconnections that defines a desired brightness in each operating mode.

The electronic circuitry may also distinguish between: i) removal of theprimary supply from the primary input connection by a user opening aswitch coupled, in use, to the lighting device; and ii) primary supplyfailure; and, upon detection of primary supply failure, may providepower from the secondary power supply to one or more light sources ofthe lighting device to provide emergency lighting functionality.

The electronic circuitry may comprise a memory, preferably anon-volatile memory, for storing user configured parameters defining adesired brightness of light in each operating mode, so that the desiredbrightness can be recalled during a subsequent operation in that mode.

Another aspect also provides a lighting device comprising: first andsecond light sources; a primary input power connection for receivingprimary power from a primary power supply, for powering the first lightsource; a secondary input power connection for receiving secondary powerfrom a secondary power supply, for powering the second light source; andelectronic circuitry arranged to control power delivery to the first andsecond light sources using power received at the input powerconnections; wherein the electronic circuitry is configured todistinguish between: i) removal of the primary supply from the primaryinput power connection by a user opening a switch coupled, in use, tothe lighting device; and ii) primary supply failure; and, upon detectionof primary supply failure, is configured to provide power from thesecondary power supply to the second light source to provide emergencylighting functionality; and wherein the electronic circuitry is userconfigurable so that in a first configuration power from the secondarypower supply is only provided upon detection of primary supply failureand so that in a second configuration power from the secondary powersupply is provided to the second light source while primary power issupplied to the first light source.

The first light source may be powered by an AC primary power supply andwherein the second light source may be powered by a DC secondary powersupply.

The electronic circuitry may receive a data signal over a wirelesscommunications link or through one or more of the input powerconnections that sets the electronic circuitry in the first or secondconfigurations.

Another aspect provides a lighting device comprising: one or more lightsources; a primary input power connection for receiving primary powerfrom a primary power supply, for powering a light source; a secondaryinput power connection for receiving secondary power from a secondarypower supply, for powering a light source; and electronic circuitrycoupled to the input power connections and arranged to control powerdelivery to the one or more light sources using power received at theinput power connections; wherein the electronic circuitry comprisessensing circuitry configured to sense an external impedance connected tothe primary input power connection and an isolator for isolating thesensing circuitry from other components of the lighting device at leastwhen said sensing circuitry is sensing said external impedance.

The isolator may comprise a semiconductor junction device, such as azener diode, which isolates the sensing circuitry from other componentsof the electronic circuitry. The semiconductor junction device may becoupled to the primary input power connection and connected to thesensing circuitry such that the semiconductor junction device is reversebiased when the sensing circuitry is sensing the external impedanceconnected to the primary input power connection.

The sensing circuitry may apply a measurement voltage to the primaryinput power connection and the amplitude of the measurement voltage islower than the breakdown voltage of the semiconductor junction device.

Alternatively, the isolator may comprise a relay device that isolatesone or more of said light sources from the sensing circuitry.

These and other aspects of the invention will become apparent from thefollowing description of exemplary embodiments which are described belowwith reference to the accompanying Figures in which:

FIG. 1 is a schematic view of one embodiment of a lighting device forconnection to a conventional lamp holder and wiring installation andwhich can provide a backup light function in the event of mains failure;

FIG. 2 is a schematic diagram illustrating the connection of thelighting device shown in FIG. 1 in a typical wiring installation;

FIG. 3 is a block diagram illustrating the main components of electroniccircuitry forming part of the lighting device shown in FIG. 1;

FIG. 4 is a schematic diagram illustrating the electrical connection ofa sensing circuit and a switch mode power control unit forming part ofthe circuitry shown in FIG. 3;

FIG. 5 a is a plot illustrating a sequence of voltage pulses generatedby the sensing circuitry shown in FIG. 4;

FIG. 5 b illustrates a sense signal sensed by the sensing circuitryshown in FIG. 4 obtained when primary power input terminals of thecircuitry shown in FIG. 4 are connected to a high impedance;

FIG. 5 c illustrates a sense signal sensed by the sensing circuitryshown in FIG. 4 obtained when primary power input terminals of thecircuitry shown in FIG. 4 are connected to a low impedance load;

FIG. 5 d schematically illustrates the components of a window comparatorforming part of the sensing circuitry shown in FIG. 4;

FIG. 6 illustrates the way in which two lighting devices can operate ina master/slave configuration;

FIG. 7 is a circuit diagram illustrating the way in which a processorforming part of the circuitry shown in FIG. 3 may be powered either froma power signal derived from a primary power supply or by a power signalderived from a secondary power supply;

FIG. 8 illustrates a circuit having two back-to-back MOSFET switchesused to provide load control between primary and secondary powersupplies.

FIGS. 9 a, 9 b and 9 c illustrate alternative arrangements for couplinga sensing circuit and a power supply unit of the circuitry shown in FIG.3 to a mains input supply;

FIG. 10 is a schematic view of an alternative lighting device embodyingthe present invention;

FIG. 11 a illustrates an in-line adaptor embodying the present inventionwhich can provide emergency lighting upon mains power failure to aconventional light source;

FIG. 11 b schematically illustrates an in-line adaptor which issemi-permanently installed and controls power delivery to a pendantlight attached thereto;

FIG. 12 schematically illustrates an embodiment in which electroniccircuitry like that shown in FIG. 3 is built into a power supply unitused for powering conventional low voltage lights; and

FIG. 13 schematically illustrates an embodiment in which electroniccircuitry like that shown in FIG. 3 is provided in a remote controldevice and used to control the operation of one or more lightingdevices.

OVERVIEW

FIG. 1 shows an example of a lighting device 1 embodying the presentinvention. In this instance, the lighting device 1 is in the form of atraditional look-a-like light bulb that has an opticallytransparent/translucent housing 3 that is mechanically coupled to afitting 5. The fitting 5 is for connecting the lighting device 1 to aconventional lamp holder (in this case illustrated as a conventionalscrew type holder), which in turn connects the lighting device 1 to aprimary power supply.

One or more light sources 7 are provided within the transparent housing1. In this embodiment, the light sources 7 include a plurality of lightemitting diodes 9. In this example, the multiple light emitting diodes 9are arranged in one or more arrays 11 so that the lighting device 1 hasa wide angle of illumination. To achieve optimum efficacy, efficiencyand life span, the LED array(s) 11 are mechanically fixed and thermallyconnected to a heatsink 13. The structure and function of the heatsink13 is described in the applicant's earlier GB application (GB1014428.5), the content of which is incorporated herein by reference. Asshown in FIG. 1, the heatsink 13 has a cavity 15 in which a battery 17is mounted. As will be explained in more detail below, the battery 17 isfor powering the light source(s) 7 in the event of a mains powerfailure.

Electronic circuitry 19 is provided within a base 21 of the lightingdevice 1. The electronic circuitry 19 includes circuitry for sensingwhen there is a primary power failure and circuitry for coupling thebattery 17 to the light sources 7 to provide light during such a primarypower failure. In most installations, the lighting circuit (in which thelighting device 1 will be installed) will include one or more manuallyoperable switches for allowing the user to switch on and off thelighting device 1. Therefore, the electronic circuitry 19 is able tosense when such switches are open and when they are closed. The way inwhich this sensing is performed will be described in more detail later.

Lighting Circuit

FIG. 2 is a schematic diagram illustrating a typical electricalinstallation 12 in which the lighting device 1 shown in FIG. 1 may beinstalled. As illustrated in FIG. 2, local or national grid supplied ACpower is typically transformed down from a very high transmissionpotential D, usually in the order of thousands of volts, to a lower“mains” supply voltage by a transformer 14. The secondary winding of thetransformer 14 will provide power to one or more local consumers acrossterminals 16, here representing the external connections into a building18. This input supply (shown as potential E) usually passes through oneor more appropriate current limiting protection devices 22 (fuses,circuit breakers etc.) which are typically mounted within a distributionboard, consumer unit or the like. As shown in FIG. 2, two lamp holders24-1 and 24-2 are connected within a lighting circuit 28 to the currentlimiting devices 22 via user operable switches 26-1 and 26-2. In thisillustration, the switches 26 are shown in a two-way configuration,although there may only be a single switch 26 or multiple switchesconnecting the holders 24 to the current limiting devices 22. Thus,lighting devices 1 mounted in such lamp holders 24 will have a mainspower supply as the primary power supply for illuminating the lightsources 7.

As shown in FIG. 2, the impedance within the building 18 between thesupply terminals is represented by the impedance (Z) 30. This impedance30 is created by loads such as other electrical appliances and otherdevices that are connected to the incoming power supply at terminals 16,via the current limiting protection devices 22. It is this impedance 30(optionally together with the impedance of the current protectiondevices 22 and the impedance of the transformer 14) that creates auseful detectable difference in impedance of the lighting circuit 28when the user operable switches 26 are in the open and closed states.

Thus when mains power is removed from a lighting device 1 mounted in oneof the lamp holders 24, the lighting device 1 can detect if the switches26 are open circuit or closed circuit by measuring the impedance acrossits primary supply terminals 32 and thus determine if the mains powerhas been removed by a power failure or by a user switching one of theswitches 26. Various different approaches can be taken in order tomeasure this impedance and hence to determine the positions of themanually operable switches 26. As will be explained in more detailbelow, the approach taken should ensure that measurements taken by onelighting device 1 do not interfere or detrimentally affect the operationof another lighting device mounted in the same lighting circuit 28 andcontrolled by the same switches 26 or on the same supply circuit aspotential E. Additionally, care should be taken to ensure that whenmultiple lighting devices 1, like the one illustrated in FIG. 1, areconnected to the same lighting circuit 28, measurements by one lightingdevice 1 do not interfere with the measurements of other lightingdevices 1. The preferred way in which this is achieved is described inmore detail later.

Operating Modes

In this embodiment, the lighting device 1 has a number of differentmodes of operation and the current mode of operation is typicallydetermined based on external conditions of the power supply to thelighting device 1. From the discussion above, the supply itself may becategorised into three states: power present, power not present when thesupply is open circuit (high impedance), and power not present when thesupply is closed circuit (low impedance).

Primary Mode of Operation

The primary mode of operation is defined to occur when there is aprimary power supply electrically connected to the fitting 5 that canprovide electrical energy to illuminate the light source(s) 7 andthereby produce useful light. During this primary mode, the battery 5may also be intelligently (re)charged as required using energy from theprimary power supply, typically via a step-down transformer, switchedmode power supply or other voltage reducing and rectifying subsystem.The charging of the battery 17 is controlled by the electronic circuitry19 which monitors the charge rate and cell voltage to preventovercharging or over rapid-charging.

During the primary mode of operation, electrical power is being providedby the primary power supply and therefore, there is no power failure.Accordingly, it is not necessary for the electronic circuitry 19 tosense the impedance of the supply lines to determine if any useroperable switches are opened or closed. Therefore, the sensing can beinhibited during this primary mode of operation. However, such sensingmay be optionally continued, if desired, and any results ignored sincethe impedance is unlikely to be measurable when the primary power ispresent.

Secondary Mode of Operation

During the secondary mode of operation, the lighting device 1 isconfigured to produce useful light using power from a secondary powersupply (in this case from the battery 17). The lighting device 1 is setinto this mode for the duration that the lighting device 1 is connectedto the primary power supply via the fitting 5 and there is an absence ofprimary power and the processing electronics 19 determines that there isa low impedance (typically below 5 k ohms) between the supply lines. Themeasurement of the supply impedance may be made continuously,periodically, randomly or pseudo randomly. Such random or pseudo randommeasurement may also help to avoid interference with other similarlighting devices 1 connected in the same lighting circuit (for examplemultiple lights controlled by a common light switch, such as achandelier). The way that the multiple lighting devices 1 can operatetogether will be described in more detail later.

In this preferred embodiment, the processing electronics 19 are arrangedso that if the lighting device 1 is connected electrically via fitting 5to a low impedance load, the lighting device is arranged to enter thissecondary mode of operation and therefore to cause the lighting device 1to generate light using power from the battery 17. This allows thelighting device 1 to be tested for demonstration, diagnostic or otherpurposes—for example by shorting the supply terminals on the fitting 5with a suitable low impedance electrical connection (such as a user'shand). The processing electronics 19 can also set the lighting device 1into its secondary mode of operation during diagnostic testing or inresponse to an input command received, for example, from an externaldevice.

Dormant Mode of Operation

In the dormant mode of operation, the lighting device 1 is configured toemit no useful illumination, although the electronic circuitry 19 ispartially active. The lighting device 1 is configured to enter thedormant mode of operation for the duration that there is no primarypower input via the fitting 5 when the lighting device 1 is connected toa lighting circuit 28 and when there is a high impedance load connectedto the supply lines (typically above 10 k ohms). Again, the measurementof this impedance may be made continuously, periodically, randomly orpseudo randomly. The lighting device 1 exits the dormant mode when mainspower is restored across the mains supply terminals (in which case itreturns to the primary mode discussed above) or if the sensing circuitrysenses a low impedance load connected to the main supply lines whilstthere is still no mains power (in which case it returns to the secondarymode discussed above).

As will be described in more detail later, in this preferred embodiment,the electronic circuitry 19 employs various energy saving techniques andcircuit components that minimise the power drawn by the electroniccircuitry 19 from the battery 17 during the dormant mode of operation.

Sleep Mode of Operation

In the sleep mode of operation, the lighting device 1 is configured toemit no useful illumination and the electronic circuitry 19 is arrangedto make no impedance measurements. The sleep mode of operation may beentered after the lighting device 1 has been in the dormant mode ofoperation for a predetermined period of time (for example six months),or should the battery charge fall below a low threshold level, or whenit is signalled to do so by an external device or by the user applyingcertain predefined conditions on the lighting device 1—such as byswitching primary power to the lighting device 1 six times in a threesecond period. Detection of the mains signal may be made, for example,by detecting that the signal received at the primary supply terminalshas a frequency within an expected frequency range (for example between40 Hz and 70 Hz). The lighting device 1 is preferably set into its sleepmode as the default condition when it is manufactured, such that thereremains no or minimal drain on the battery 17 until the product isinstalled by the user. The lighting device 1 may be “woken” from thesleep state by, for example, applying primary power to the lightingdevice 1.

When the device changes state from primary mode to secondary mode whenthe primary supply is removed, the lighting device 1 instantly switchesto secondary mode (light on) whilst it measures external conditions.This ensures that there is no flicker or interruption to illuminationduring a power failure. If the measurements indicate that the switches26 are open circuit, then the lighting device 1 will turn the lightsources 7 off and enter the dormant mode. Similarly, when operating inthe secondary mode and the lighting device detects a mains signal at theprimary supply terminals, the lighting device 1 does not immediatelyenter primary mode—instead it waits and confirms that the mains supplyis stable before returning to the primary mode.

Diagnostic and Mode Indicators

In this embodiment, the lighting device 1 has a diagnostic indicator 23in the form of a light emitting diode that is connected separately tothe electronic circuitry 19. The electronic circuitry 19 can control thediagnostic indictor 23 to either continuously or intermittently indicatethe current operating mode and/or to indicate any fault detectiontherein. This may be achieved, for example, by varying the illuminationof the diagnostic indicator 23 or, if multiple different LEDs areprovided with different colours, these can be illuminated to indicatedifferent diagnostic states.

Remote Control

As shown in FIG. 1, the preferred lighting device 1 also includes acommunication transducer 25 that can receive signals from and transmitsignals to another device (not shown) that is remote from the lightingdevice 1. These external signals may be used, for example, to controlthe operation of the lighting device 1, if diagnostic testing orconfiguration by a remote operator is desired. The communicationtransducer 25 may be, for example, an optical transducer (such as aninfra-red transducer) or an acoustic or an electromagnetic transducer(such as an RF transceiver) which can communicate with the remote deviceusing corresponding wireless signals. The remote device can be a simplebattery or otherwise powered hand held controller having a number offunctional buttons (or the like) for allowing a user to input controlcommands to the lighting device 1.

This remote control feature may be used, for example, to vary thebrightness of the light generated by the lighting device 1. This can beachieved, for example, by varying the power (current and/or voltage)applied to the light source(s) 7. Alternatively, if the light source(s)7 are arranged in different groups, with the light source(s) 7 in eachgroup being independently powered by the electronic circuitry 19, thenthe brightness can be varied by varying the number of light source(s) 7that are simultaneously powered.

The communication transducer 25 can also be used to communicate thestatus and/or diagnostic information to the remote device. For example,the electronic circuitry 19 may be arranged to monitor the charge statusof the battery 17 and this remaining charge status may be signalled tothe remote device via the communication transducer 25.

The communication transducer 25 can also be used to receive userprogramming information input via an external device for storage withina memory of the electronic circuitry 19. This user programming coulddefine, for example, emitter brightness in primary and/or in secondarymodes of operation or the frequency or manner in which self-diagnostictests and results are performed and signalled via the diagnosticindicator 23. The remote control signal can also be used to turn on thelighting device 1 even when there is no power failure or when the useroperable switches 26 are open circuit. This function could be used, forexample, in a building scenario where a central control stationinstructs a plurality of lighting devices 1 within the building toswitch on at a defined level of illumination for night time illuminationpurposes.

Electronic Circuitry

FIG. 3 is a block diagram illustrating the main components of theelectronic circuitry 19 used in this preferred embodiment. As shown, thecircuitry 19 includes a power supply unit 31 that is connected toprimary supply terminals 33 provided in the fitting 5, for connection tothe mains supply; and secondary supply terminals 34 for connection tothe positive and negative terminals of the battery 17. The power supplyunit 31 is configured to transform the primary supply voltage, forexample by step-down transformer, switch mode power supply or othervoltage reducing and rectifying subsystem; and to provide power derivedfrom the primary supply (or if it senses that there is no primary supplyat the supply terminals 33, to supply power from the battery 17 viaterminals 34) to a processor 35 that controls the operation of thelighting device 1. The power supply unit 31 also provides the powerrequired for illuminating the light source 7.

The electronic circuitry 19 also includes sensing circuitry 37 which isconfigured to sense the impedance across the primary supply terminals33; a charging circuit 39 for charging the battery 17 via the terminals34; a diagnostic module 41 for performing the various diagnostic testingdiscussed above and for controlling the diagnostic indicator 23 viaterminal 43; and a communications module 45 for communicating withremote devices via the communication transducer 25 connected viaterminal 47.

As shown in FIG. 6, in this embodiment, the electronic circuitry 19 alsoincludes two output drivers 50-1 and 50-2 that are controlled by theprocessor 35 and that provide the desired drive currents for driving thelight sources 7 via output terminals 49 and 51. In this embodiment, thelight sources 7 are arranged in two groups, with the light sources 7 ineach group being driven by a respective one of the output drivers 50.Thus, in this embodiment, the processor 35 can switch on the lightsources 7 in both groups at the same time or the light sources 7 ineither one of the groups by controlling the respective output drivercircuits 50. The processor 35 can also vary the brightness of the lightsources 7 in each group by setting a desired drive power for each outputdriver circuit 50.

In the block diagram illustrated in FIG. 3, the different modules areshown as being separate modules from the processor 35. In practice, thefunctionality of many of the modules shown in FIG. 3 will be softwaremodules run by the processor 35 or a mix of software and hardware. Themodules have been illustrated in the form shown in FIG. 3 for ease ofunderstanding the functions and operation of the different modules. Amore detailed description of the various modules will now be given.

Processor

In this embodiment, the processor 35 is at the heart of the electroniccircuitry 19 and controls the operation of all of the modules shown inFIG. 3. The processor 35 may be based on an ASIC device but ispreferably a programmable processor (such as a PIC microcontroller)having memory and software that defines its operation. Such softwarecontrolled processors are easier to update with improved software oradditional functionality after installation. During the primary mode ofoperation, the processor 35 is powered from a voltage derived from theprimary supply; and in the secondary and dormant modes of operation itis powered by a voltage derived from the battery 17.

Charging Circuit

The charging circuit 39 is provided to monitor the charge status of thebattery 17 (via the power supply unit 31) and to charge (or recharge)the battery 17 when needed. By monitoring the charge status of thebattery 17, the charging circuit 39 can ensure that the battery 17 isnot overcharged. The charging circuit 29 can also signal the presentbattery charge status to the diagnostic module 41 for historicalrecording and analysis (such as to adjust brightness levels for a givenminimum duration e.g. 3 hours) and/or for output to the user either viathe diagnostic indicator 23 or via the communication transducer 25. Inthis embodiment, the charging circuit 39 also manages battery usage inthe secondary mode of operation, so that the battery charge is notcompletely exhausted—resulting in battery damage. Therefore, in thisembodiment, the charging circuit signals the processor 35 to stopemergency illumination when the battery charge falls below a definedlower threshold level.

Diagnostic Module

The diagnostic module 41 performs various diagnostic tests and presentsthe diagnostic results to the user via the diagnostic indicator 23. Thediagnostic results can also be stored within a memory (not shown) of theprocessor 35 to maintain an historical record of the operation of thelighting device 1. The diagnostic module 41 may interact with thecharging circuit 39 in order to obtain battery charge status informationand with the sensing circuitry 37, the communication module 45 and theoutput drivers 50 to confirm correct operation thereof. The operation ofthe diagnostic module 41 can be controlled by the user either viasignals received using the communication transducer 25 or other signalscommunicated, for example, over the primary supply via terminals 33.

Communications Module

The communications module 45 is operable to control communicationbetween the lighting device 1 and an external device via thecommunication transducer 25. The communications module 45 is responsiblefor performing any required modulation and demodulation of the data tobe transmitted to and received from the remote device. For example, thecommunications module 45 may transmit diagnostic data obtained from thediagnostic module 41 to a remote device for remote monitoring of theoperation of the lighting device 1. Alternatively, user configurationdata may be received from the remote device and programmed into theprocessor 35.

Output Driver

The output drivers 50 are controlled by the processor 35 and generatethe driving currents (or voltages) required to drive the light sources7. The output driver 50 used will depend on the technology andconfiguration of the light source(s) 7 being driven. In this embodiment,the light sources 7 are LEDs and the output drivers 50 can becommercially available integrated circuit LED drivers having featuressuch as efficient Pulse Width Modulation (PWM) current feedback drivingof the LEDs, whether individually or in one or more “strings”. Eachoutput driver 50 is controlled (independently or as a single entity) bythe processor 35 and can generate a respective different drive current(or voltage) at its output terminals 49/51. The output drivers 50 obtaintheir power for generating the drive signals from supply voltagesgenerated by the power supply unit 31.

Sensing Circuitry and Power Supply Unit

As shown in FIG. 3, the sensing circuitry 37 is configured to sense theimpedance across the primary supply terminals 33 via the power supplyunit 31. The way in which this connection is made and the way in whichthe sensing circuitry 37 performs the measurement, in this preferredembodiment, will now be explained with reference to FIG. 4. As shown inFIG. 4, the sensing circuit 37 is connected to the primary supplyterminals 33 via isolating resistors 61 and 63, which prevent theprimary supply from damaging the sensing circuitry 37. When the sensingcircuitry 37 wishes to make a measurement of the impedance across thesupply terminals 33, the sensing circuitry 37 applies a measurementvoltage across the supply terminals 33, which may be referenced to orisolated from the ground potential. The magnitude of this measurementvoltage is preferably between 1 and 9 volts and typically at a voltagelevel similar to that provided by the battery 17 (such as 3 volts). Thisis much smaller than the magnitude of the mains supply voltage which isan AC voltage having an RMS value typically between 88 volts and 265volts. As will become apparent from the following description,therefore, when the mains supply voltage is present at the terminals 33,the sensing circuitry 37 is not able to use the measurement voltage tosense the impedance across the supply terminals 33. However, this is notimportant as there is no need for the electronic circuitry 19 to measurethe impedance across the supply terminals 33 when the primary supplyvoltage is present. Indeed, in the preferred embodiment, the processor35 inhibits the sensing circuitry 37 from generating the measurementvoltage during the primary mode of operation, when the supply voltage ispresent across the terminals 33. The presence of the supply voltage maybe detected, for example, by checking that the mains voltage levelacross the primary supply terminals 33 is within predefined limits ofexpected values of the voltage or by checking that the frequency of thesupply voltage is within expected values of frequency, for example, bychecking that the primary supply voltage has a frequency above 40 Hz andbelow 70 Hz.

As shown in FIG. 4, the primary supply terminals 33 are connected to abridge circuit 69 which converts the AC supply voltage into a DC voltagewhich is input to a switch mode power control module 71 via a zenerdiode 73. The switch mode power control module 71 then converts theinput DC voltage into the appropriate output voltages required forpowering the other components of the electronic circuitry 19 and forpowering the light source(s) 7.

The reason for using the zener diode 73 will now be explained. Asdiscussed above, the purpose of the sensing circuitry 37 is to sense theimpedance across the supply terminals 33. However, the supply terminals33 are connected both to the lighting circuitry 28 (shown in FIG. 2) andto the circuit components of the power supply unit 31 and the rest ofthe electronic circuitry 19. Therefore, if the power supply unit 31and/or the other circuitry in the lighting device 1 provide a lowimpedance path between the supply terminals 33, then the sensingcircuitry 37 may mistakenly interpret that user operable switches 26 inthe lighting circuit 28 are closed (low impedance) when in fact they areopen (high impedance). Therefore, in this embodiment, the zener diode 73is used in order to provide isolation between the sensing circuitry 37and the rest of the electronic circuitry 19. This isolation is achievedbecause the magnitude of the measurement voltage is less than the zenerdiode breakdown voltage and therefore the zener diode 73 provides a highimpedance to the sensing circuitry 37 (or at least to the measurementvoltage). Of course, when the primary voltage is applied across thesupply terminals 33, the rectified DC voltage applied across the zenerdiode 73 is much larger and will be greater than the breakdown voltageof the zener diode 73. Therefore, when the primary supply voltage ispresent at the terminals 33, the rectified voltage from the bridgecircuit 69 passes through the zener diode 73 to the switch mode powercontrol module 71. Similar isolation can be achieved using othersemiconductor junction devices—for example using a number of diodesconnected in series such that the voltage drop across all of the diodesis greater than the measurement voltage, or if the measurement voltageis lowered below the breakdown voltage of a conventional diode, then thezener diode 73 may be replaced with a conventional diode.

As shown in FIG. 4, a capacitor 75 is connected across the primarysupply terminals 33. This capacitor 75 is conventionally used to improvethe performance of lighting devices in terms of EMC compliance andperformance and the like. In this preferred embodiment, however, thecapacitor 75 is also used by the sensing circuitry 37 when determiningthe impedance between the supply terminals 33. In particular, thecapacitor 75 offers a known circuit component for the sensing circuitry37 to detect as a reference and allows for self-test verification of itssensing functionality.

Measurement Process

As mentioned above, when the sensing circuitry 37 performs ameasurement, it applies a measurement voltage across the supplyterminals 33. In this embodiment, to minimise the risk of interferencebetween similar lighting devices 1 on the same lighting circuit and tominimise the energy drawn from the battery 17 when making themeasurements, the sensing circuitry 37 generates a measurement signal 65that comprises a sequence of voltage pulses 67 (which are illustratedhere as being square wave pulses, but they could have different pulseshapes). During each voltage pulse 67, charge will be stored on thecapacitor 75 which will then decay over time once the voltage pulse 67has ended. The rate at which the charge on the capacitor 75 accumulatesand then decays depends on the impedance across the supply terminals 33and hence on the state of the user operable switches 26.

FIG. 5 shows a number of graphical representations of the transmittedpulses 67 (FIG. 5 a) and the corresponding charge (voltage) across thecapacitor 75 that results (FIGS. 5 b and 5 c). FIG. 5 a illustrates thevoltage pulses generated by the sensing circuitry 37. The duration (T0)of each voltage pulse 67 is typically in the order of milliseconds andthe period (T) between pulses is typically in the order of 0.1 to 10seconds. FIG. 5 b illustrates the way in which the voltage across thecapacitor 75 accumulates and then decays over time when the manuallyoperable switches 26 are in their open (high impedance) state; and FIG.5 c illustrates the way in which the voltage across the capacitor 75accumulates and then decays over time when the manually operableswitches 26 are in their closed (low impedance) state. As can be seen bycomparing the plots shown in FIGS. 5 b and 5 c, the rate at which thevoltage across the capacitor 75 accumulates and then decays depends onthe impedance across the supply terminals 33 and hence in dependenceupon the state of the manually operable switches 26. Therefore, thesensing circuitry 37 can sense the present state of the manuallyoperable switches 26 by monitoring the voltage across the capacitor 75.There are various ways in which the sensing circuitry 37 can performthis monitoring and some of these will now be discussed.

One technique for sensing the state of the switches 26 is illustrated inthe left hand waveforms of FIGS. 5 b and 5 c respectively. In thistechnique, the sensing circuitry 37 measures the time taken for thedecaying voltage to fall from point W1 (corresponding to a known voltageV1 across the capacitor 75) to a point W2 (corresponding to a knownvoltage V2 across the capacitor 75); and then compares the determinedtime (T1 in the case of the plot shown in FIGS. 5 b and T2 in the caseof the plot shown in FIG. 5 c) against a predetermined threshold. If thedetermined time is above the threshold, such as is the case for the plotshown in FIG. 5 b, then the manually operable switches 26 are determinedto be in the open state; whereas if the determined time is below thethreshold, such as is the case for the plot shown in FIG. 5 c, then itis determined that the manually operable switches 26 are in the closedstate.

The predetermined threshold value that is used in the determination maybe a factory set constant or it may be adapted depending on theinstallation in which the lighting device 1 is installed. For example,the sensing circuitry 37 may be arranged to sense the variation inimpedances over a predefined period and detect the minimum value ofmeasured time and the maximum value of measured time. The thresholdvalue can then be set somewhere in the middle between these two times.Alternatively, during an installation procedure, the user may berequested to switch the manually operable switches 26 on and off anumber of times (when the primary supply is isolated from the lightingcircuit) so that measurements can be obtained when the switches 26 areopen and when they are closed. An appropriate threshold value can thenbe determined for the given installation. Since the impedance 30 withinthe building or on the lighting circuit 28 may change over time, thesensing circuitry 37 can keep a running average value for the highimpedance measurements and a running average value for the low impedancemeasurements that it makes and then use these average values to re-setthe threshold value from time to time.

The threshold potentials V1 and V2 used in this technique may also befactory set threshold values or they too may be dynamically set during acalibration routine for the lighting device 1 once it is installed inthe lighting circuit 28. The values are preferably chosen so as to yielda reliably wide spread in measured times between the open and closedstates of the manually operable switches 26.

An alternative measurement technique is illustrated in the right handplots shown in FIGS. 5 b and 5 c. In particular, in this technique thesensing circuitry 37 is arranged to measure the time taken for thevoltage across the capacitor 75 to fall from its measured maximum value(V3) at point W3 to a point W4 at which the potential as fallen to avalue V4 which is a set fraction (for example one fifth) of the peakpotential V3. Thus, as before, when there is a high impedance connectedacross the supply terminals 33 (when the switches 26 are open), themeasured time, T3, will be greater than the threshold, and conversely,the measured time, T4, will be below the threshold when there is a lowimpedance across the supply terminals 33 (when the switches 26 areclosed).

With either of the techniques described above, the sensing circuitry 37preferably uses a window comparator, such as the window comparator 81shown in FIG. 5 d (which may be implemented in hardware and/orsoftware). In this case, the input voltage V in (which is the voltageacross the capacitor 75) is input to two comparators 83-1 and 83-2. Incomparator 83-1, the input voltage is compared with the high voltagereference value (corresponding to the voltage V1 for the first techniqueor the measured maximum capacitor voltage V3 in the second technique)and in the other comparator 83-2, the input voltage is compared againstthe low voltage reference value (corresponding to voltage V2 in thefirst technique or voltage V4 in the second technique). The outputsignal V out from this window comparator 81 will be at a low level whenthe input voltage is between the two reference levels and will be at ahigh value otherwise. The sensing circuitry 37 can then measure thetimes T1 and T3 as being the time between the falling edge and therising edge of the output voltage V out.

A further alternative method for sensing the impedance across the supplyterminals 33 is only to use a single measured value on the falling edgeof the capacitor voltage. In particular, given that the sensingcircuitry 37 knows both the duration T0 and the amplitude V0 of eachmeasurement voltage pulse 67, then a fractional proportion of thisamplitude value may be taken as the timing end point. Thus, the sensingcircuitry 37 may calculate the time taken for the voltage across thecapacitor 75 to fall to the given threshold value from the rising orfalling edge of the voltage pulse 67. Alternatively still, the sensingcircuitry 37 may simply measure the instantaneous voltage across thecapacitor 75 at a predetermined time after the rising or falling edge ofthe measurement voltage pulse 67. When the impedance across the supplyterminals 33 is large, the measured voltage will be larger than when theimpedance across the supply terminals 33 is small. However, suchabsolute measurements are not preferred as they are more susceptible tonoise and measurement error. Indeed, in the preferred embodiment, oncethe sensing circuitry 37 has made an initial determination of the stateof the manually operable switches 26, the sensing circuitry 37 thencompares the measurements obtained from successive measurement voltagepulses 67 in order to detect a change of state of the manually operableswitches 26. It does this by detecting a significant change in themeasured times from one measurement to the next. Once the sensingcircuitry 37 detects a change of state of the manually operable switches26, it performs a number of additional measurements to confirm thechange of state before changing the operating mode of the lightingdevice 1. These additional measurements are used in case the firstmeasurement that indicated the change of state is caused by noise ormeasurement error, or in case it conflicts with measurement signal(s)from one or more other similar lighting devices 1.

Interference between Multiple Lighting Devices

As mentioned above, multiple lighting devices 1 (like the one shown inFIG. 1) may be connected in parallel on a given lighting circuit 28,such as in a multiple fitting luminaire, chandelier or the like. Eachlighting device 1 will generate its own set of measurement pulses 67 forimpedance sensing when they are in the dormant and secondary modes ofoperation. When a measurement voltage pulse 67 is applied across thesupply terminals 33 by one lighting device 1, the connection of theother lighting devices 1 will provide an apparent additional capacitiveload measured across the supply terminals 33 (because of capacitor 75).This will change the charge rate and the decay rate of the capacitorvoltage measured by the sensing circuitry 37. Therefore, again, duringan appropriate calibration routine, the sensing circuitry 37 can refine,as appropriate, a threshold used to maximise the sensing accuracy of thesensing circuitry 37. From the charge up rate, the sensing circuitry 37can also estimate the number of other similar lighting devices connectedon the same lighting circuit 28 (since it knows the capacitance value ofthe capacitor 75 and it can assume that similar capacitors will beprovided in the other lighting devices).

As mentioned above, the duration (T0) of each measurement voltage pulse67 and the time period (T) between pulses are preferably selected so asto minimise the chances of two lighting devices 1 (which are connectedin the same lighting circuit 28) from applying measurement voltagepulses 67 to the primary supply terminals 33 at the same time. Inparticular, if the period T is much greater than the duration T0 of eachvoltage pulse 67 (in this example embodiment, it is between 100 and 1000times greater) then it will be quite rare for two or more lightingdevices 1 to apply their measurement pulses across the supply terminals33 at the same instantaneous point in time. The chances of suchcollisions can be reduced further by randomly or pseudo randomly varyingthe time period T between success measurement pulses 67. This may beachieved, for example, by using a constant period T and by adding orsubtracting a randomly or pseudo randomly varying amount at eachmeasurement point. The combination of this random amount and variationsin the clock frequencies between the lighting devices 1 (an inherentdifference between physical manufactured components) will likely reducefurther the possibility of two or more lighting devices 1 applying theirmeasurement pulses 67 across the supply terminals 33 at the same time.

In the rare event that other lighting devices 1 do apply theirmeasurement pulses 67 across the supply terminals 33 at the same or atsimilar times, an incorrect reading will be obtained. However, asmentioned above, in the preferred embodiment the sensing circuitry 37uses the measurements obtained from a number of measurement pulses 67before taking a decision. This means that the measurement obtained froma single pulse will not be used in isolation and therefore, errorscaused by such simultaneous (or overlapping) measurements by otherlighting devices 1 should not cause the lighting devices 1 to operateincorrectly, hence provide reliable operation.

In addition to varying the pulse period, T, to avoid collisions withother lighting devices 1, the pulse period T may also be varied forother purposes. For example, when the sensing circuitry 37 initiallydetects a change in the impedance across the supply terminals 33, thesensing circuitry 37 may shorten the period between successive pulses inorder to confirm that the changed circuit impedance is both valid andsustained before the decision is taken to change the operating mode ofthe lighting device 1.

Conversely, the period between measurement voltage pulses 67 may beintelligently extended over time in order to conserve battery power. Inparticular, when the lighting device 1 is last switched from its primaryoperating mode (or its second operating mode) to its dormant operatingmode, then the sensing circuitry 37 may be arranged to measure theimpedance across the supply terminals 33 at a normal repetition periodT. However, if the operating state of the lighting device 1 does notchange during an extended period of time (for example for a number ofweeks or months) then the sensing circuitry 37 may be arranged to extendthe interval between measurement voltage pulses 67. Typically, thenormal period (T) between measurement pulses voltage 67 is between 50and 500 milliseconds; this period may be extended to, for example, theorder of seconds. Delaying the measurement pulses in this way willsignificantly reduce the power drawn from the battery 17 during thedormant mode of operation, at the expense of a slight delay in switchingon the emergency lighting when needed. The period between measurementvoltage pulses 67 may also be made dependent on the charge state of thebattery 17. In particular, as the charge on the battery reduces, theprocessor 35 may signal to the sensing circuitry 37 in order to increasethe interval (T) between measurement voltage pulses 67. In this way, thedrain on the battery 17 can be minimised.

Master/Slave Operation

When there are multiple lighting devices 1 (such as those shown inFIG. 1) on the same lighting circuit 28 or in the same locality,interference between the lighting devices 1 may be reduced further bymaking one of the lighting devices 1 a master lighting device, whichperforms impedance measurements and by making the other lighting devices1 slave devices, which do not perform impedance measurements. Such amaster/slave pair of lighting devices is illustrated in FIG. 6. Themaster lighting device is designated 1-M and the slave is designated1-S. In this case, when the master lighting device 1-M determines thatthere is a power failure and that the manually operable switches 26 arein the closed state, it signals to the other slave lighting devices 1-Sthat they should enter their secondary modes of operation so that theywill generate light using power from their internal batteries 17.Communication between the lighting devices 1 may be achieved using theircommunication transducers 25. Alternatively, the master lighting device1-M may signal the other lighting devices 1 that are connected to thesame lighting circuit 28 by applying a communication signal across thesupply terminals 33. This communication signal may be modulated on to asuitable carrier frequency that will allow the slave lighting devices1-S to differentiate the communication signal from any primary supplysignal received at the supply terminals 33.

When the communication transducers 25 are used to communicate betweenthe lighting devices 1 and one or more of the slave lighting devices 1-Sare out of range of the master lighting device, one or more of the otherslave devices 1-S that are within communication range of the masterlighting device 1-M may operate as repeaters or relay devices in orderthat messages to or from the master lighting device 1-M can becommunicated with such “out of range” slaves.

In order to limit interference caused by the electronic circuitry 19 ofthe slave lighting devices 1-S, each lighting device 1 may also includea relay or similar isolation or interruption device 77 that candisconnect its excitation circuitry 19 from the supply terminals 33. Inthis way, if a lighting device 1 has been configured as a slave device,then it will activate the isolation device 77 in order to isolate itselectronic circuitry 19 from the supply terminals 33 in all operatingmodes except the primary operating mode. In this way, when the slave(s)and the master lighting devices 1 are in the dormant or secondary modesof operation, the master 1-M will perform the impedance measurements andall of the slave lighting devices 1-S will effectively be open circuitbetween the supply terminals 33 due to the isolation device 77. If themaster lighting device (or some other device) determines that theoperating mode should be changed, then the master lighting device 1-Msignals the change of state to the slave lighting devices 1-S whichadapt their operating modes accordingly. If the slave lighting devicesare returned to their primary mode of operation, then they willdeactivate the isolation device 77 so that the electronic circuitry 19of the slave device 1-S is again connected to the supply terminals 33.

Therefore, as those skilled in the art will appreciate, the provision ofsuch an isolation device 77 in each of the slave devices 1-S can improvethe effectiveness or efficiency of the impedance sensing due to removingpossible interference created by the slave devices. Additionally,utilising only one lighting device as the master means that batterydrain is minimised (at least on the slave lighting devices). Theprovision of such an isolation device 77 in a conventional light bulbwould also be advantageous—as it would prevent any low impedance paththrough the conventional bulb form interfering with the measurementsmade by the master to determine if the light switches 26 are open orclosed circuit. Such a light bulb would not have a battery or thesensing circuitry, although it would still need some form of intelligentPSU device to ensure the correct switching in and out of the isolationdevice 77, when the master is performing its measurements. In such anembodiment, in the event of primary light failure, only the lightdevices that have a battery or other secondary power supply wouldprovide emergency illumination and the other lighting devices that donot have the secondary power supply would not.

With regard to determining which lighting device 1 is the master andwhich lighting devices are the slaves, this selection can be made by theuser, for example setting configuration data in each lighting device 1,for example by sending configuration signals to each lighting device 1using the communication transducer 25. Alternatively, the selection maybe made automatically depending on the order of connection to thelighting circuit 28. In one embodiment, the role of master lightingdevice 1-M is rotated between multiple lighting devices in order toequalise battery consumption across the different lighting devices 1.For example, the master lighting device 1-M may be programmed to polleach of the slave lighting devices 1-S in order to determine theircurrent battery charge. Depending on the result of this poll, thecurrent master lighting device 1-M (or an external device) may determinethat one of the slave lighting devices 1-S should become the master andan appropriate handover be performed.

Power Control Circuitry

As discussed above, the electronic circuitry 37 is powered either from avoltage generated from the primary supply across terminals 33 or fromthe battery 17. Switching circuitry is therefore needed to select eitherthe DC voltage derived from the primary supply or battery voltage fromthe battery to power the light array(s) 11 and/or the circuit componentsof the electronic circuitry 19.

The circuit arrangement shown in FIG. 7 can automatically allow thehighest potential difference from either the primary source potential V(obtained by rectifying the primary supply voltage and output from theswitch mode power control module 71 or from some other PSU); or thesecondary source potential W (obtained from the battery 17), to providecontinual electrical power to the processor 35 and the other electroniccomponents of the lighting device 1. As shown, the circuitry includestwo diodes 90-1 and 90-2, with the input of diode 90-1 being connectedto the primary power supply potential V and the input of diode 90-2being connected to the secondary power supply potential W obtained fromthe battery 17. As shown, the supply potential for the processor 35 isconnected to the outputs of both diodes 90. Therefore, the processor 35will draw its power either from the supply potential V or from thesecondary battery potential W depending on their instantaneous values.Therefore, the circuit arrangement effectively provides a simpleuninterruptible power supply (UPS) arrangement.

Other system elements (including the light source or array(s)) inaddition to or instead of the processor 35 may be powered using thecircuit arrangement shown in FIG. 7 (or variations of it). However incertain circumstances, particularly when the circuit arrangement is topower the light array(s), the voltage drop across the diode 90 is likelyto cause inefficiency, especially when operating from the battery 17since this voltage drop may represent a significant portion of thevoltage available from the battery 17.

Thus any switching arrangement for switching between primary power andsecondary (battery) power is required to have minimal voltage drop oroperation inefficiency; whilst preventing the battery power supply fromdischarging to the primary power supply circuitry. In other words,sufficient full-isolation should be present to prevent connection of thebattery directly to the mains-derived DC supply, otherwise there will beno control over the charging of the battery using power from the primarysupply.

To avoid the voltage drop associated with the simple diode arrangementof FIG. 7, in the preferred embodiment, the circuitry 92 shown in FIG. 8is used to control the drawing of battery power from the battery 17.Similar circuitry 92 may also be provided to control the drawing ofpower from the primary supply voltage(s) output from the switch modepower control module 71. As shown, the load control circuitry 92 has twoinverse series connected metal oxide field effect transistors (MOSFETs)93-1 and 93-2 arranged in a novel way to provide load control whilstpreventing reverse current when in an inactive state. The inverseconnection of the two MOSFETs overcomes the internal body diodeproperties inherent with any MOSFET device 93 which would otherwise leadto an undesirable voltage drop and/or current flow through the MOSFETs93 when they are turned off.

As shown, the circuitry 92 includes an input terminal 94, a controlterminal 96 and an output terminal 98. Input terminal 94 is the powerinput terminal which is connected to the battery 17 via terminals 34(and illustrated here as being at potential X). The control terminal 96is an active-low input for controlling the output from the load controlcircuitry 92, such that applying a negative potential with respect tothe input terminal 94 (shown as potential Y) results in a positiveoutput potential at the output terminal 98 (shown as potential Z) thatis, in practice, marginally below the potential (X) at the inputterminal.

Impedance device 100 (typically a resistor) provides a source of powerto the control terminal 96 from the input terminal 94. This is relevantin the event of other system elements, such as the processor 35,entering a long-term hibernation or ‘sleep mode’ for prolonged orsustained periods, for example due to low battery charge levels, untilthe primary power supply next becomes available. This impedance device100 therefore keeps the control input terminal 96 close to the inputpotential (X) when the feeding control circuit (e.g. the processor 35)for control terminal 96 is in a high impedance or disconnected state.This ensures that the MOSFETs 93 remain off and thus maintain a highimpedance between the input terminal 94 and the output terminal 98.

As shown in FIG. 8, the two MOSFETs 93 each have a gate (labelled G), asource (labelled S) and a drain (labelled D). MOSFETs have a problem inthat there is always an inverse “body diode” inherent in the structureof the device. In order to remove this problem, two MOSFETs areconnected in series such that the drain of MOSFET 93-1 is connected tothe drain of MOSFET 93-2. This means that the inherent body diodes(illustrated and labelled 101-1 and 101-2 in FIG. 8) of the MOSFETswitches 93 oppose each other. This eliminates the resulting issue ofreverse current flow through the body diode when the MOSFET is notswitched on. When the MOSFETs 93 are switched on, the voltage dropacross the pair of MOSFETs is minimal and presents no problem to theoperation of the circuit. This is a significant saving when compared tothe normal battery voltage or the mains supply derived voltage(s)generated by the switch mode power control module 71 (which is typicallya few volts). A similar advantage can be achieved if the MOSFETs 93 areconnected so that the source of one MOSFET is connected to the source ofthe other MOSFET.

Therefore, by employing two opposing MOSFETs 93 in this manner, there isno problem of voltage drop across the MOSFETs 93 when they are switchedon, and when the MOSFETs 93 are in a high impedance state, the tworeverse-connected body diodes 101 prevent current flow between the inputterminal 94 and the output terminal 98 caused by a potential differencebetween the primary power supply (obtained via the switch mode powercontrol module 71 or otherwise) and the secondary power supply obtainedfrom the battery 17.

Self Test Diagnostics

Diagnostic module 41 can be configured to perform self-tests forverification and diagnostic purposes. These may be performedcontinuously or intermittently based upon a time interval, or otherwiseby command or event such as upon user demand through signals receivedvia communications module 45 or the like. Alternatively, throughmonitoring circuit conditions which may include historical stored dataand or real time measured values, such as relating to the charging andor discharging performance of the battery 17 or other secondary storagedevice, the tests may be intelligently scheduled at an appropriate timeswhich, for optimum operational efficiency, may depend upon the currentmode of operation of the system.

Tests may include software analysis of data collected over any period oftime by processor 35 or other components of the circuitry 19. Forexample, in the case of verifying function and sufficient performance ofbattery 17 or the like, analysis may be executed using data collectedfrom measurements of battery voltage and rate of change over time,either during times of charging by the charging circuit 39 (at whichtime the charge current may instead or in addition be measured bycharging circuit 39 or otherwise, for subsequent use as a input data forthis analysis), and or during periods when the battery 17 is not beingcharged.

The analysis may include applying an optional load to the battery 17 toaffect a discharge of stored potential therein, thus providing theopportunity to acquire more relevant data measurements such as rate ofdecay of potential difference etc. This load could be a known loadexclusively for this purpose, such as a designated switchable resistor,but may be the light source(s) 7 itself, a load which may be internallymeasured or approximated from known hardware parameters. In this case,the system may be operating in any mode, but preferably during eitherprimary or secondary modes of operation during which light emission isalready required and therefore such a test would go unnoticed. If thetest is performed during the primary mode of operation, the battery 17would provide some or all electrical power to operate the lightsource(s) 7 for a limited period of time over which data is collectedfor battery analysis. Such testing may be performed intermittentlyaccording to either automatic time scheduling (such as relating to datacollected for age or amount of use), or manually (such as according toprevious or historical test results, or even upon user demand). Thistesting may instead or additionally be performed in the case where,depending upon the battery technology being used, it is advantageous forthe secondary power supply to be periodically partially or fullydischarged, for purposes of extending battery life expectancy ormaintaining performance through use cycling. Such a strategic full orpartial discharge represents an ideal opportunity for combining bothbattery conditioning and/or maintenance with performance analysis aspart of a diagnostic testing routine.

A full or substantial discharge is not desirable in terms of ability tooperate in secondary mode during a power failure, hence such anoperation is preferably limited to infrequent occurrence and upon userdemand, such as in the case where emergency lighting regulations mayrequire a test of duration performance. Alternatively a partialdischarge test may provide sufficient data for an estimation of thebattery capacity (either full potential or remaining) to be ascertainedand displayed or communicated via diagnostic module 41 or communicationsmodule 45.

Advantageously, if the testing is performed during secondary mode whenthere is already a load present on the battery 17 (of the lightsource(s) 7), analysis of battery discharge can be performed toascertain battery performance. Further advantageously, such a testingroutine may additionally be used to predict or estimate the likelycapacity remaining. Such information may, through control by processor35 or otherwise, intelligently adjust the power taken from the batteryto achieve or optimise current draw to ensure that the emergencylighting will give a minimum duration of lighting, which may be adjustedperiodically or constantly with such an aim in mind. Alternatively, sucha capacity remaining or duration estimate may simply be stored or usedand in some way communicated to the user, such as via diagnostic module41 or communications module 45.

Modifications and Alternative Embodiments

In the above embodiment, a zener diode 73 was used to isolate thesensing circuitry 37 from the other components of the electroniccircuitry 19 when the sensing circuitry 37 is making its impedancemeasurements. Various other techniques can be used to achieve a similarisolation. For example a relay or transformer could be used to performthe desired isolation. FIG. 9 illustrates three alternative arrangementsusing power supply transformers to isolate the sensing circuitry 37 fromthe other components of the electronic circuitry 19 when makingimpedance measurements. With these transformer designs, the transformeris used to step down the primary supply voltage to a lower voltage whichcan then be smoothed and converted into a DC voltage using a similarbridge circuit 69 to the one shown in FIG. 4. Whilst such transformerbased isolation solutions are less sophisticated than the mainembodiment described above, they do offer the advantage that theyprovide isolation between the sensing circuitry 37 and the primary powersupply and isolation between the sensing circuitry 37 and the othercomponents of the electronic circuitry 19.

In the arrangement shown in FIG. 9 a, a transformer 82 having primarypower supply (J) connected to its primary winding 84 and havingsecondary winding 86 divided into two parts—having a main secondarywinding 86-1 that provides a step down potential K and a tertiarywinding 86-2 that connects to the sensing circuitry 37. Operationally,during the primary mode when a supply potential J is present, thepotential K (or the combined potential K+L) is used to provide the usualpower for the electronic circuitry 19 and for powering the light sources7. During the dormant and secondary modes, however, the primarypotential J is no longer applied and the sensing circuitry 37 appliesthe measurement pulses across terminals L of the secondary winding 86-2.These pulses will, through normal magnetic flux operation of thetransformer 82, induce signals into the primary winding 84. Theconnection of any circuitry across K will remain constant and thereforecan be disregarded. Thus, changes in high or low impedance across J canbe measured across L whilst remaining electrically isolated. Therefore,the sensing circuitry 37 can detect changes in the impedance of thelighting circuit 28 in which the lighting device 1 is connected, such asmay result from the user switching on or off the user operable switches26.

FIG. 9 b illustrates an alternative transformer arrangement, where twotransformers 82-1 and 82-2 are connected in series across the primarypower supply having potential M. The operation of this embodimentremains the same as that described above for FIG. 9 a, with power takenacross N in the primary mode and pulses being transmitted through P whenthe impedance sensing is being performed by the sensing circuitry 37during the dormant and secondary modes. FIG. 9 c alternatively shows aconventionally deployed transformer 82 providing potential difference Rfrom the primary power supply input Q during the primary mode ofoperation; and a coil of wire 88 being placed around or in proximity toa connection of the primary winding 84 such that pulses applied across Sresult in currents being induced in the primary power supply lines. Theinduced current will depend on the impedance of the primary supply lineswhich will in turn induce a back EMF across S which can be sensed by thesensing circuitry 37.

In the above embodiment, the lighting device included a battery 17 forproviding a backup or secondary power supply in the event of primarypower supply failure. The battery can be of any technology, replaceableor non-replaceable and multiple batteries may be provided connected inseries and/or in parallel. Each battery itself may comprise a singlecell or multiple cells as appropriate to the battery technology. Where amulti cell battery is used, the charger may be arranged to monitor andcharge each cell individually or groups of cells as desired.Alternatively, instead of using one or more batteries 17, other chargestorage devices may be used to provide a secondary power supply, such asa capacitor. However, batteries are preferred since they can providesecondary power over a longer period of time. The secondary storagedevice is preferably mounted internal to the lighting device, but it canbe mounted externally if desired. In one embodiment, the battery can beisolated from the electronic circuitry 19 so that the lighting devicecan only operate in its primary mode of operation. This may be done inresponse to a received user input or in response to detecting a batteryfault or a fault in another system component.

In the above embodiment, the sensing circuitry 37 generated voltagepulses which it applied across the supply terminals 33 in order tomeasure the impedance across the supply terminals 33. In an alternativeembodiment, the sensing circuitry 37 could include a current generatorand could instead apply pulses of known current to one or both of thesupply terminals 33 and could then measure the voltage across the supplyterminals to determine a measure of the impedance between the supplyterminals 33.

In the above embodiments, the light sources that were used in thelighting device 1 were LEDs. As those skilled in the art willappreciate, the use of LEDs is preferred given the ease with which theycan be controlled (e.g. output intensity), their long expected operatinglife, rough handling ability and of particular advantage (given thebattery-operation likelihood of the device) their low power consumption.However, the light sources can be formed from any lighting technology,such as compact fluorescent tubes, incandescent lighting (such ashalogen lighting) etc.

In the above embodiment, the lighting device took the form of a normallook-a-like light bulb. However, the lighting device can also take theform of an elongate tube similar to the common fluorescent “strip light”variety.

In the above embodiment the battery is mounted within a cavity of a heatsink used to extract heat from the light sources. As those skilled inthe art would appreciate, the mounting of the battery and the use ofthis particular heat sink is not essential. The battery may be mountedin any convenient location and the heat sink can have any desired formor can be omitted if desired. When the heatsink is provided, it may beformed from an electrically conductive material and coupled to acapacitive sensing circuit that can thus sense when a user touches orcomes into close proximity to the heatsink. For example, the heatsinkmay include a one or more electrically conductive plates (which may alsoact as cooling fins) that are electrically connected to a chargemeasuring circuit. The measuring circuit can then determine a valuebased upon charge measurement techniques (well known to those skilled inthe art), which value will change in the event that the capacitive fieldis interrupted or altered, such as by a user touching or entering a partof his or her body in the vicinity to the plates. This user input can beused, for example to control the operation of the lighting device, suchas to control the operating modes or to control the brightness of thelamp in dependence upon a measured time that the user approaches ortouches the heatsink. Other technologies may also be used to performthis proximity sensing, such as short range radar devices.

In the embodiment described above, the lighting device includeddiagnostic and communication circuitry. As those skilled in the art willappreciate, this circuitry is not essential and could be omitted ifdesired. Additionally, one or more user switches or inputs may bemounted on the lighting device. This user input can be used to cause thelighting device to enter a given mode of operation or to enter userconfigurations or to initiate a diagnostic or self-test.

In the above embodiment, the lighting device included a communicationsmodule 45 that was able to communicate with external devices using acommunication transducer 25. In an alternative embodiment, thecommunications module 45 may be arranged to communicate with theexternal devices by receiving and/or transmitting signals over thelighting circuitry 28 in which the lighting device 1 is installed. Suchcommunication signals would be transmitted at a different frequency tothe mains signal in order that the communication signals can beseparated from the mains signal. Instead of or in addition to using thecommunication transducer 25, the electronic circuitry 19 couldcommunicate with one or more remote devices by varying the lightproduced by the light sources 7. For example switching them on and offin dependence upon the data to be transmitted. A receiver in the remotedevice would recover the data by detecting the variation in the lightproduced by the light source(s) 7. Regardless of the communicationtechnique employed, various different standard communication protocolscould be used for the communications between the lighting device and theremote device(s).

In the main embodiment described above, the electronic circuitry 19included a diagnostic module 41 for performing diagnostic tests and forcontrolling diagnostic indicators 23 to indicate the diagnostic testresults. As discussed, the diagnostic test could be used, for example,to determine the remaining charge capacity of the secondary power supply(e.g. the battery 17), which could be indicated via a coloured indicator23 or pulse variations of an LED indicator 23. A problem with thisarrangement is that when the lighting device 1 is producing usefullight, this general illumination is likely to mask the visibility of thediagnostic indicator(s) 23. This problem can be overcome, however, bydeploying the diagnostic indicator(s) 23 for a period of time shortlyafter the lighting device 1 stops producing useful light (for examplewhen the lighting device transitions from its primary mode of operationinto its dormant mode of operation). Alternatively the light array(s)may be partially or fully employed to act as an information indicatorfor diagnostic, status, fault, condition or other purposes. For example,the light generated by the light array(s) 11 could be pulsed dependingon the remaining battery charge, as measured and controlled by theelectronic circuitry 19. The user can optionally configure the way inwhich this is achieved by storing appropriate user configurationparameters within the electronic circuitry—for example using a remotecontrol device that communicates with the device using the communicationtransducer 25.

In the above embodiment, a user was able to set various userconfigurable parameters of the lighting device 1 using the communicationtransducer 25 and a remote control device. Alternatively, the lightingdevice 1 may have an additional configuration or ‘setup mode’ thatallows certain simple configurations to be defined, choices selected andchanges saved upon exit, all via changes in the primary power suppliedto the lighting device 1 made by the user opening and closing the useroperable switches 26. For example, the electronic circuitry 19 may bearranged so that if the user switches the primary power supply to thelighting device 1 three times within 3 seconds, it will enter a setupmode, and one cycle within the next five seconds thereafter to select aspecific option etc. Such a configuration technique would be simple andcheap to implement and would allow the user to select certain othercontrol parameters defining the unit's operation. This can include, butis not limited to defining: emitter brightness in primary or secondarymodes, and the change in illumination quantity during secondary modeover time or according to the electrical charge remaining in thesecondary power supply etc.

In the above embodiment, the lighting device 1 had a number of lightsources of the same type (in this case LEDs) arranged into two groupsthat were independently driveable by the electronic circuitry 19. FIG.10 illustrates an alternative embodiment that has different types oflight sources, each being of varying design, type, technology or thelike. The general operation of this embodiment is the same, with theexception that the two or more types of light emitters may beadvantageously utilised to achieve several improvements over theembodiment shown in FIG. 1. These improvements include, reduction inpower consumption verses quality and quantity of light output,manufacturing cost, and built-in redundancy for an increased margin ofsafety or component lifespan. In particular, this arrangement allowslight sources that are optimised for primary illumination to be usedwhen the primary supply is present and allows light sources that areoptimised for emergency lighting (requiring lower power to drive them)to be used when there is a power failure. Additional advantages of thismulti-emitter approach include potential for extended product life andsafety margins through built-in redundancy, particularly critical foremergency lighting systems, with scope for system separation within theelectronic circuitry 19 in which the primary emitter remains for useonly during primary mode.

In the embodiment shown in FIG. 10, the two different light sourcescomprise an LED array(s) 91 and a compact fluorescent tube 93 withassociated ballast circuitry 95. Electronic control circuitry 19 isjoined, by connection 97 (comprising typically two wires), to fitting 5such that the primary supply may provide electrical power for operatingthe LED array(s) 91 and/or the compact fluorescent tube 93 in theprimary mode, with the same connection 97 being utilised for impedancesensing to ascertain external circuit conditions as before. Anappropriate secondary power supply (such as battery 17) can provideback-up power as before for powering at least the LED array(s) 91.

The electronic circuitry 19 may control combinations of the lightsources 91 and/or 93, such as utilising compact fluorescent tube 93 forprimary mode operation when the primary power supply is available(potentially augmented by light from the LED array 91), and utilisingthe LED array(s) 91 as the sole emitter during secondary mode when theprimary power supply is interrupted and only the secondary power supplyis available. In this embodiment, the compact fluorescent tube 93 may bepowered directly by the AC primary supply in the primary mode ofoperation. This can be achieved by replacing the output driver 50 usedfor the fluorescent tube 93 with a relay switch that is directlyconnected between the primary input power terminals 33 and thefluorescent tube 93 and that is controlled by the processor 35 or thepower supply unit 31.

In this embodiment, the electronic circuitry 19 may include circuitry todetect, for example, if the light source normally used for primaryillumination is faulty or has failed. If so then the electroniccircuitry 19 can use the other light source for primary illuminationinstead. The electronic circuitry 19 can detect such a failure either bymeasuring the impedance across the terminals of the light source (andinferring from this measure if the light source is operational) or usinga photo-sensor that can detect if the light source is actually producinglight or using current measurement techniques.

In the main embodiment discussed above, the lighting device 1 was asingle unitary device. In alternative embodiments, some of thecomponents and some of the functionality may be moved to another devicewhich controls the powering of a lighting device (such as a conventionalbulb). This may be achieved, for example, using an in-line adapter thatsits between a conventional light bulb and the lamp holder. Such in-lineadapter embodiments are illustrated in FIG. 11. As shown, the in-lineadapter 101 sits between the primary power supply 103 and a conventionallighting device (or devices) 105. The in-line adapter 101 may be areadily interchangeable device such as the arrangement shown in FIG. 11a, or a permanent installation such as the example shown in FIG. 11 b.

The in-line adapter 101 will typically have the same electroniccircuitry 19 as in the first embodiment, enclosed within a suitablehousing or casing 107. This can then be retrofitted to an existinglighting circuit by connecting the fitting 5-1 of the in-line adapter101 into an appropriate vacant lamp holder 24 providing mechanical andelectrical connection to the primary power supply 103. A plurality oflamps or lighting devices, shown here as a single conventional lightbulb 105 having light fitting 5-2, mechanically and electricallyinterface with a lamp holder 109 that forms part of the in-line adapter101.

During primary mode operation, a switching device 113 such as amechanical or solid-state relay controllable by the electronic circuitry19 allows power from the primary power supply from 103 to be routed tothe lamp holder 109 for purposes of powering the light bulb 105. Thisswitching device 113 may be controlled by the electronic circuitry 19,and is an important requirement specific to this in-line adapterembodiment, since the required impedance sensing technique for detectingexternal switch positions cannot be reliably performed when certaintypes of conventional light bulbs (ones having a low internal impedance)are connected across the primary supply terminals 103—as the presence ofsuch a conventional low impedance light bulb may cause the sensingcircuitry 37 to determine that the manually operable switches 26 areclosed circuit when in fact they are open circuit. Thus, when impedancemeasurements are to be made, the switching device 113 is activated todisconnect the conventional light bulb 111 from the supply 103.

An additional feature that can be performed by the electronic circuitry19 in this embodiment (because of the presence of the switching device113) is that it can allow the illumination of the light sources 91 onthe in-line adapter 101 during the primary mode without illuminating theconventional light bulb 105. This could be triggered by signals receivedfrom an external device such as from an external user-controlled remotecontroller, using the communication transducer 25 shown here for exampleconveniently integrated within the LED array 91.

The electronic circuitry 19 may also have the ability to detect thefailure or removal of the light bulb 105 from the adapter 101, so thatif the primary power supply is available to the in-line adapter 101, theelectronic circuitry 19 can still provide useful illumination using theLED array 91 powered from the primary power supply. Sensing that thelight bulb 105 has failed or been removed from the adapter 101 can beachieved by various methods, including measuring the electricalimpedance across or current through terminals of the lamp holder 109. Inparticular, when the light bulb 105 has failed or been removed from theholder 109 there will be a high impedance across the terminals of thelamp holder 109. This high impedance can be detected by applying a testvoltage across the input terminals of the lamp holder 109 (when the lampholder 109 has been isolated from the rest of the primary supply 103(using the switching device 113) and sensing the current drawn.Alternatively, a low current drawn by the lamp holder 109 when theprimary supply 103 is supplied to the terminals of the lamp holder 109is also indicative of a failed or removed light bulb 105. Such lowcurrent draw can be detected by measuring the voltage drop across apurposely included resistor (not shown) that is connected in series withthe terminals of the lamp holder 109, or by using any other currentsensing transducer.

Instead of using such an electrical detection method (for detecting afailed or removed light bulb 105), one or more light sensors may insteadbe employed to measure external ambient light levels. One suchphoto-sensitive semiconductor device 117 is shown in FIG. 11 a,conveniently integrated within the LED array 11. This photo-sensitivesemiconductor device 117 can be controlled and monitored by theelectronic circuitry 19, and used to ascertain if light bulb 105 isproducing useful illumination by way of monitoring the change in lightlevels before and after switching device 113 is activated to connect thelamp holder 109 to the primary power supply 103. If no appreciableincrease in light level is observed then there is a high likelihood thatlight bulb 105 has failed or been removed from its holder 109.

Regardless of the detection method used, such a feature is desirable inmission critical deployments, and greatly increases the reliability andversatility of the in-line adapter 101 in its primary mode of operation.In particular, when the adapter 101 initially detects the failed lamp,it can automatically switch on the secondary light source(s) 11 to givethe user a visual warning that the primary light bulb 105 hasfailed—even though the light is switched off at the switch 26. Thisinitial warning can then be switched off by the user, for example, byswitching the switch 26 on and off. Thereafter, every time the userswitches on the switch 26, illumination will be provided by thesecondary light source(s) until the primary light bulb 105 has beenreplaced. Further, the provision of backup emergency illumination whenthe light bulb 105 has failed or been removed provides light for theuser when they are replacing the failed or removed light bulb 105.

The photo-sensitive semiconductor device 117 may additionally beutilised to perform other specialist functions as may be selected by theuser, or pre-selected within preferences stored in memory of theelectronic circuitry 19 via an external control device such asuser-operable remote controller that communicates with the in-lineadapter 101 via the communication transducer 25. Specialist functionscould for example include the ability for the light bulb 105 and/or theLED array 91 to provide illumination from any available power supply fora predetermined time interval when ambient light levels have (prior tothe provision of the illumination) been measured to fall below one ormore threshold values over time.

An alternative embodiment of an in-line device 101′ is illustrated inFIG. 11 b, in which the in-line adapter 101′ is incorporated inproximity to or within the ceiling rose forming the usual junction forelectrical connection and mechanical suspension of a pendant light 111(as shown), multiple lamp chandelier or the like. The operation of suchas system remains the same as that outlined for FIG. 11 a.

Thus light array 91 may provide more prominent illumination, in thesecondary mode or otherwise, due to its advantageous positioning abovethat of the pendant light bulb 111. In this illustration, the lightarray 91 is formed from a plurality of individual LED emitters 9arranged in multiple rings to utilise the additional space created bydetachment of lamp holder 109 via the lighting cable 121. Furthermore,the aesthetic design constraints of such an in-line device 101′ areharmonised since it may be at least partially housed in enclosuressimilar to existing hardware and or using conveniently available spacevoids, here shown partially located within the ceiling juncture 123.

The in-line device 101′ shown in FIG. 11 b is designed to be installedon a more permanent basis. Therefore, fitting 5-1 has been replaced witha suitable electrical interface that enables electric wires or cable tobe connected thereto. The example illustrated in FIG. 11 b shows such anarrangement, with a plurality of terminal blocks 125 housed withinenclosure 127 which may or may not be integral to the main enclosurehousing 107 of the in-line adapter 101′. If the enclosure 127 isseparate from the main housing 107 of the in-line adapter 101′, then anadditional detachable interface may be included to interconnectcomponents within enclosures 127 and 107. This yields the advantage ofallowing convenient interchangeability of such a semi-permanent in-lineembodiment, including the ability of the in-line adapter 101′ tooptionally retrofit an existing interface such as a pre-installedceiling rose that permits straightforward interchange of varioussuspended lighting devices to be utilised without manual electricalinstallation. Further advantages include a greater accessibility to themain housing 107 allowing easier battery 17 replacement, and naturallythe safety and time advantages in not having to make permanentelectrical connections between the in-line device 101′ and the primarypower supply 103.

In the main embodiment described above, the electronic circuitry 19 usedfor controlling the lighting device was mounted within the housing ofthe lighting device itself. In an alternative embodiment, the electroniccircuitry 19 used to control the light sources may be provided in aseparate housing. Such an embodiment would allow the invention to beable to operate, for example, with conventional “low voltage” lamps.Such a conventional low voltage lamp typically comprises multiple lowvoltage light emitters forming a plurality of luminaries. Thesehistorically featured incandescent lamps, usually tungsten halogentechnology, although retrofit LEDs in traditional lamp holders, such asthe GU series holders, have been available in recent years. Such lowvoltage lighting systems typically utilise a supply potential differencebelow 50 volts (either AC or DC) provided by a power supply unit (PSU),which usually comprises a conventional transformer or switch mode powercircuit. The PSU is typically fed by a mains power supply which it thenconverts and supplies for powering one or more lighting devices.Unfortunately, the lighting device 1 shown in FIG. 1 does not directlylend itself to retro-fitment into such a low voltage lighting system.Apart from the overall size of the lighting device 1, the main problemis that the PSU unit that powers the low voltage lighting will inhibitthe usual impedance sensing performed by the sensing circuitry 37because there is no direct connection to the primary power supply on theinput side of the PSU. One workaround to this problem is to rearrangethe wiring of the lighting circuit 28 such that any user operableswitches are located on the output side of the PSU rather than on theinput side. However, as well as the additional effort required toperform the rewiring, such an arrangement will also mean that the mainssupply is constantly fed into the PSU input and this will invariablycause inefficiency due to heat losses associated with the PSU.

On the other hand, if the conventional low voltage PSU is replaced by amodified PSU that contains at least the main components of theelectronic circuitry 19 shown in FIG. 3, then this will overcome theseproblems. Such an embodiment is schematically illustrated in FIG. 12. Asshown, the electronic circuitry 19 is mounted in a separate housing 131that can be placed anywhere on the lighting circuit 28 so that thesensing circuit 37 can sense the impedance across the primary powersupply terminals 33. In this case, the housing 131 also includes asecondary power supply in the form of a battery 17. The outputterminal(s) 49 and/or 51 (shown in FIG. 3) from the electronic circuitry19 are then directly connected to the conventional low voltage lampholder(s) 133 and thus the low voltage lights 134 will be powered eitherby power derived from the primary supply and/or from power derived fromthe secondary supply (the battery 17 in this example). In such anembodiment, the secondary power supply (such as the battery) may bemounted in the same housing 131 as the electronic circuitry 19 or it maybe provided separately, for example, within a loft or ceiling space andconnected to the electronic circuitry 19 at terminals 34. The secondarypower source may provide power directly to the low voltage lights orthrough a voltage-transforming PSU or the like (not shown).

The housing 131 may include additional output terminals 49 that receiveconverted supply signals in the usual way (i.e. converted from the ACmains voltage to the required DC supply voltage)—so that lights attachedto these additional output terminals do not receive emergency power fromthe battery back-up in the event of a primary supply failure. In thisway, the modified PSU 131 may control a number of lamp holders 133, butmay only provide emergency lighting to a subset of those lamp holders.

Instead of the light source(s) being directly connected to the outputterminals 49 of the electronic circuitry 19 in housing 131, theelectronic circuitry 19 may transmit control signals using acommunication transducer 25 to the lighting device(s) to instruct themto power their light source(s) using secondary power from its ownsecondary power supply (such as its own battery). FIG. 13 illustratessuch an embodiment. As before, the communication transducer 25 can be ofany type—such as electromagnetic (e.g. RF or infra-red) or acoustic.Control signals transmitted from the electronic circuitry 19 in thehousing 131 would be received by a corresponding communicationstransducer 25 mounted in the lighting device 1. In this embodiment, theelectronic circuitry 135 mounted in the lighting device 1 does not needto have the sensing circuitry 37. It only needs communication circuitry45—to be able to communicate with the electronic circuitry 19 mounted inthe remote housing 131; a power supply unit 31—for controlling theapplication of power either from the primary supply or from the lightingdevice's own associated secondary power supply 17 and the appropriateoutput driver(s) 50 or relays. As those skilled in the art willappreciate, communication between the lighting device 1 and thecircuitry in the housing 131 may be two way—so that, for example, thelighting device 1 can acknowledge receipt of control signals back to thecircuitry within housing 131. Such two way communication also allowsremote testing of the lighting device 1, for diagnostic or self testpurposes without the need for physical contact. For example, the controlsignals may instruct the lighting device 1 to perform a self test and tooutput diagnostic results via the diagnostic indicator 8 or to transmitthe results back to the circuitry in the housing 131. The informationtransmitted back to the housing 131 may also include operationstatistics for the lighting device 1—such as time periods between beingin its different operating modes, measured impedance values etc.

The housing 131 may also include a user interface (keypad, displayswitches etc.) that allows a user to enter control commands, userconfigurations etc., for controlling the lighting devices 1 with whichthe circuitry in the housing 131 is arranged to communicate.

Instead of transmitting the control signals over a wireless link, theelectronic circuitry 19 mounted in the housing 131 may transmit thecontrol signals over the mains supply lines to the lighting device(s) 1.In this case, if any of the manually operable switches 26 are opencircuit, the lighting device 1 will not receive the control signal. Butthis does not matter as the user is not expecting the emergency lightingto come on when the manually operable switches 26 are open circuit. Oncethe switches 26 are closed, the lighting device 1 will receive thecontrol signal (which may be continuously or intermittently transmittedby the circuitry in the housing 131) and thus turn on its emergencylighting using power from its secondary power supply.

As a further alternative, the circuitry in the housing 131 could bearranged to transmit a control signal whilst the primary supply ispresent at its input and to stop transmitting the control signal ifthere is a power failure. In such an embodiment, the circuitry inhousing 131 would not need its own secondary power supply 17. As long asthe lighting devices 1 receive the control signals from the circuitry inthe housing 131, they will know that primary power is available(although perhaps switched off at a user operable switch 26). If thelighting device 1 stops receiving the control signal, then it can assumethat primary power has been lost and it can either directly illuminateits light source(s) from its secondary power supply or it can first tryto sense if any of the user operable switches 26 are open circuit first,before using power from the secondary power supply (of course in thiscase, the electronic circuitry 135 in the lighting device would requirethe sensing circuitry 37).

As a further alternative to this embodiment, the electronic circuitry 19mounted in the housing 131 does not need to sense the impedance acrossthe supply lines. If the housing 131 is mounted close to the main fusesor circuit breakers 22 of the building, then the circuitry in thehousing can detect the power failure simply by sensing if there is anymains power. If mains power is lost, then the circuitry in the housing131 can signal the loss of power to the lighting device(s) 1.Advantageously, this can be signalled over the lighting circuit 28—sothat if the switches 26 are open circuit, the control signal will notreach the lighting device 1 and so they will not produce their emergencylighting. However, if the switches 26 are closed, then they will receivethe control signal and can automatically switch on their light source(s)using power from the secondary supply.

In one embodiment, local or national control centres may be provided tocontrol the lighting devices 1 in different buildings. For example,control signals may be sent to lighting devices 1 in order to inhibittheir operation—for example by disconnecting their light sources fromthe primary supply terminals 33 using an appropriate isolating devicesuch as a relay. Thus, even if the user switches on the light switch,the lighting device 1 will not produce light. This could be used, forexample, to switch off lights in a building at night. Conversely, one ormore lighting devices may be remotely controlled to switch on in orderto illuminate a given area. These remote control devices may be standalone devices or they may be part of a larger system—such as an alarmsystem. For example, in the event that a fire is detected in a building,the lighting devices 1 in that part of the building may be remotelycontrolled to switch on—to provide emergency illumination to aidoccupant escape or search and rescue. As those skilled in the art willappreciate, in any such system involving communication between a numberof different devices, they will each need an address or ID number toallow communications to be targeted to individual lighting devices 1 orat least to individual groups of lighting devices. Of course signals forall devices may be transmitted without an address—such as an “emergency”signal to cause all the emergency lighting to come on.

Optionally, one or more detection devices (e.g. smoke or fire detection)may be provided integrally within the lighting device 1 or adjacent toit and they may use the same primary power supply or secondary powersupply to operate. In such an embodiment, the secondary power source(such as a battery) may be partitioned in its deployment, for examplethrough intelligent monitoring to inhibit battery use for emergencylighting when the battery capacity falls below a threshold capacity; inorder to maintain a reserve store of power to allow continued operationof the built-in detection device(s) and in the event of detection, theprovision of emergency illumination from the battery for an adequatetime before the battery becomes completely exhausted. In this way, ifthere is a power failure, the charge in the secondary supply will not bedepleted such that emergency lighting cannot still be provided duringcritical emergency situations—such as when a fire is detected. In suchan embodiment, the lighting device 1 may include an optical or acousticreceiver that detects when the fire or smoke alarm is activated and inturn it may activate its emergency lighting functionality.Alternatively, the lighting device 1 may be signaled to activate via anelectrical control signal directly from the alarm or from a centralalarm station.

The lighting device 1 may also include an audible emitter for producingan audible alarm in the event of an emergency that is able to augmentemergency illumination when a signal has been received and or anemergency condition detected. The audible alarm may be powered by eitherprimary or secondary power sources according to user configurableparameters.

Optionally, the alarm may also augment emergency illumination when apower failure or other defined event has occurred. For example, anaudible sound may be generated upon change of operating state, or whencertain operating conditions (such as low battery or a device fault) aredetected. The alarm may intermittently or continuously provide the userwith an audible indication of the state or condition that triggered thealarm. This arrangement could be particularly advantageous for exampleto alert the user that a power failure has occurred when the lightingdevice has entered its secondary mode of operation, in an embodimentwhere the lighting device is arranged to provide emergency illuminationthat is of equal brightness compared to the illumination when powered bythe primary supply (which failure may otherwise go unnoticed). The alarmcould additionally be used to provide audible warning of low batterystatus such as after prolonged secondary mode operation.

In a modified embodiment, as well as the user being able to controlbrightness level during secondary mode operation, a minimum duration oflight emission may be set or preset (via remote, communications moduleor upon manufacture) and the power used by the lighting device may becontrolled by reducing light source brightness (with an optional minimumbrightness level set or preset) according to estimated or measuredbattery capacity (as determined from the above described diagnosticmethods), to ensure a minimum time period of secondary light production.With lighting regulations in mind (3 hours minimum in UK for emergencylighting) such a method could improve efficiency, optionally varyingbrightness over time to give the best compromise between brightness andduration according to accurate battery capacity estimations. Suchbattery capacity predictions determined using measured discharge datawill of course take into account degradation over time and use.

The diagnostic tests described in the first embodiment may also beimplemented to verify functionality and or performance of other systemelements, such as light source(s) 7 or individual emitters 9 or arrays11 thereof. For example, the light sensor 117 shown in the in-lineadaptor embodiment in FIG. 11 could be employed to ascertain thatcollectively the light emitters are performing to a required standard orthreshold. Measured values may alternatively be analysed and employedfor purposes of brightness adjustment or optional feedback thereof bylight source driver(s).

In a modified embodiment, as well as brightness levels produced by lightsource(s) 7 being a changeable parameter adjustable via processor 35through output driver 50 control or otherwise, optionally the colourtemperature of the light produced by light source(s) 7 may also bevaried. This can be achieved by various methods such as for an LED lightsource, changing the brightness of individual light emitters 11 and/orarrays 9 wherein arrays or LEDs therein have different colourtemperatures, thus allowing variance of the overall colour temperatureof light emitted from light source (7) within the lighting device 1.Such a variance could be advantageously utilised to allow control of thequality of light produced, such as achieving a preference of subtlecolour temperature (e.g. warm white verses cool white light) or allowinga full ‘RGB’ colour range for mood or atmospheric lighting purposes.Such control could be implemented by the user, such as through a remotecontrol device via communications module 45 or otherwise, or optionallyby the processor itself for strategic purposes such as to form a visualdiagnostic system that may replace or augment diagnostic module 41.

In the above embodiments, the lighting device 1 had a pair of primarysupply terminals for connection to a primary supply, such as a mainssupply circuit. In addition, another (separate) pair of terminals may beprovided on the lighting device for connecting the lighting device toanother power source. This other power source may be, for example, froma renewable energy source such as a photovoltaic cell or a wind turbineor the like. The power received from this additional AC or DC supply maybe used to light the light sources and/or to charge the battery 17 viaoptional additional power supply control and management circuitryinternal or external to the lighting device.

1.-64. (canceled)
 65. A lighting device comprising: one or more lightsources; a primary input power connection for receiving primary powerfrom a primary power supply, for powering at least one of the one ormore light sources; a secondary input power connection for receivingsecondary power from a secondary power supply, for powering at least oneof the one or more light sources; and electronic circuitry coupled tothe input power connections and arranged to control power delivery to atleast one of the one or more light sources using power received at theinput power connections; wherein the electronic circuitry comprisessensing circuitry connected to the primary input power connection andconfigured to sense an external impedance connected to the primary inputpower connection and an isolator for isolating the sensing circuitryfrom other components of the lighting device, the other components ofthe lighting device being electrically connected to the primary inputpower connection and presenting a low impedance across the primary inputpower connection at least when said sensing circuitry is sensing saidexternal impedance.
 66. A lighting device according to claim 65, whereinthe isolator comprises a semiconductor junction device isolating saidsensing circuitry from the other components of said electroniccircuitry.
 67. A lighting device according to claim 66, wherein saidsemiconductor junction device comprises a zener diode.
 68. A lightingdevice according to claim 66, wherein the semiconductor junction deviceis coupled to the primary input power connection and is connected to thesensing circuitry such that the semiconductor junction device is reversebiased when said sensing circuitry is sensing the external impedanceconnected to the primary input power connection.
 69. A lighting deviceaccording to claim 66, wherein the sensing circuitry is arranged toapply a measurement voltage to the primary input power connection andwherein an amplitude of the measurement voltage is lower than abreakdown voltage of the semiconductor junction device.
 70. A lightingdevice according to claim 65, wherein the isolator comprises atransformer.
 71. A lighting device according to claim 65, wherein saidisolator comprises a relay device isolating one or more of said lightsources from the sensing circuitry.